Volume control for program-distribution systems



M. E. STRIEBY VOLUME CONTROL FOR PROGRAM DISTRIBUTION SYSTEMS March 9", 19,26.v

Filed Sept. '7, 1925 AND TELEQRPH 355.91.

To all 'wliom if; may #of/morn.:

Be it known llink/li, lflnnnlrftn E. S'inimn', osding at lvlilllnn'n, in tlw county of lLsSe-x and Slime oef New Jersey', inni@ inventod mn.- nin 'improvements in '/'olnino Conti'ols for lfogx'znnlistiibuition Systems, 'ol' which lli@ 'following is speciloaion.

This invention relatos to wim piogi'ain d isibnion systems, and naoio particularly lo axiangomonts 'for 'the nminti'fnanco ol' Constant volnn'm al lie receiving slntiozw of 'rinvii syntcnns. w

ln n wir@ pi'ogf-:znn Llish-ilinion sysioni, the nsnnl ai'wngoniont is to lnwc. n minibar ol' linos oxlomling to in1l i\'idnol ioooiving sla.- lionn, snif. linnn living coi'nioc'od in parallel o the lino-liars nt o. coni'nl. oilifce. which bus lnue; in coznn'innicnion vitli n piogimn uw.. j*k power amplifier iissinlly intervenne; lwivcoon. ifm: linfa-bars anni the nrognnn somo for the nwpono o :inging the. frans-- inissimii lo 'tfno ioiioil level. Tho number olf snbsoibibeifs lines notinilly committed to the. bus-bars will. of course, vn'j' from time ilo tin and ono ioqziaiwnnont foi? satisfactory opa-Ninon oi vogjun'n systoin of *Lines lmrim no?, at Qing," sul:-

nvi'or is; limi. lio Velino@ nciiliors saion'will romain. Snlmtantialiy oonslinnnt indclpcnefloni; :my change in tlio ,m'nn'boi of stations which nrny "Je lis'ening to Elie piogazn. t

'li accordance Willi 'ilo pi'esen'i nvenlon il. i5 pioposeal lo maintain *die 'volume at. each Subsoriboils emilion subszinfialy constant by so m'iunging inu'tlfns 'lmtA tho onlipn ixnpedane@ of the power ninplilioz: will be Sinni as Compared willi tho impedance of nimload consisting oij the various snoscrilfnns lines connected 'o lili@ luis-liars in parallel. This result mug; lne. minimo@ ln: in ,iposingz n auch imho os to .make of the ai'nplil'ie: as vii-.w il l'lnfougfn o coi'nposite s.

ii'mgeclnnco of lio suoocrilwxS lino' ille. effective output .nnpoclnnco olf he nnipnnzi l rialion .in olnifno will. l not `loa noticeable io ngon'ion als@ has lli@ that. il'. pfovi les a` lain;

nzion betonen the sub- The invention may now be moreonll; im clorsi'ood by referencia to the :following de- .Lzm'ipfion thereof, when read in connection with the accompanying drawing, Figure l. of which shows Sclnlmntially. die gfeneml layout of a wir@ program system embodying zlie j/Srincipios of the invention; Fig. 2 o which shovs n simpliid circuit equivolen to tlne. ffii-cuit o1" l', and Figs. B ond of which are syinbolicnl dinginins o nid. in oxplniningj the ii'wenion.

Roforing io Fig. l, L i a, trmxli loading to a Suitable p'ioginin Source oc L typo Wall known 4in the nrt.' tinnl; in minuten in bus-bars i() to which a. plm'alitg? ol' subscriboi's lines l, L2, 910.5 may oon-- nocod in nnlltipln. A power znnpllm' U.

of any known type may be inclndoil in lli@ trunk L for the. purpose of n'np lim noglinn waives upon the subscribers' linfa@ 'in sninblo volume. Each Snbsciilfs lino ioisn'iinutes in typo suitable mission. said. at R1, R2, oto.

in order hat the cumont 'ille subscribers lines may bo for xocoving nograon 'brannrecelving se constant regardless of the nnmbel of lilieoj rn innox e1-mint of the power anipiiiiiei" P1151. and nl 1o of tlns trnnsfomner is mail@ auch t :ya

forme' `will. lre small. as compznrad. ivitl'i iii.

composito inigiedance of all. of the p fllo sul'isci'ibors linen connocled to the bnn-im l'n order 'to understand the effect. of "lio 'rrnnislfonicf T lm. givon.' 'inl-', :is fis-1min@ filmt tho 'new iinpvclanco, the output ciionit of jim poni-nu' the iansformer 'E is suoli as fo one@ impedance down lio 26 ,'onnis. Lotina filler assumo that the pedane@ of @ook on soi'iloors line is '1GO :/ln'm that'. ibo imp-eil of: each subscriber@ soi', is 2700i, if Ams, und oi* er'nnploicyu that bo'h 4iinpdanc Elmo il saine angle." The impscnoe lodging auch subscriber@ line inclif'inolly ill alien lbs. 2,100 ohms.

n receiving sei; of any known iinposzod. upon impedance of the other lines of the system which are et the moment connected to the bus-bars. The entire circuit .may he represented symbolically as shown in Fig. 3, in which an electromotive force e is applied to aanetwork consisting of. impedances ZW, Z1 and Zt.- the latter being the impedance looking into the output of the amplifier through the transformer, the impedance Z1 being the impedance looking into the subscribers line, and the impedance ZD, being the com? posite impedance of the other subscribers lines connected to the lons-hars.

If but one subscribers line is connected to the bus-bars, the impedance ZMV will be elimina-ted and I1, the current flowing into the line, may be expressed as follows:

e e i` Leserziooioes (l) H, on the other hand, the total number of lines in the system is 100 'and all are connected to the bus-bars, the impedance Z1 will be 2100 ohms and the impedance ZBD will be 2.2 ohms. The current L00, which is the current flowing in the bus-bars, may then be expressed as follows:

Lofzs (2;

In the above equation 21 represents thc resultant impedance of 100 lines connected in parallel, each having an impedance o' 2100 ohms.

The current Il, Hoiving into en individual line will be 1/ 100 part of thetotel current L00 flowing in the bus-bars, and may be expressed ns follows:

Comparing the velues given by equations (1) and (3), 1t is' seen that the current flowing in :in individual line under the two extreme conditions met with will only vary about 10%, which 4is a variation so smell that it cumstsnces, if but one line is connected to the bus-bars, the current flowing will loe given by the 'following equation:

e e. "ei-tsiocc-ie-i (4) On the other hand, if 100 lines ere connected 'to the bus-bars, the total currentlx00 Imc Comparing equations (4) und (6), it iscapparent that with only one line connected to vthe bus-bars, the volume will be almost 190% greater than when 100 linesy are connected'.

Making the impednce looking intothe output circuit of the amplifier throu h the transformer smell as compared Wit the composite impedance of the lines has the inherent advantage that ,it provides a large degree of segregation between subscribers"v` circuits. In order to understand this, let us consider again the equivalent circuit shown in Fig. 2, which represents the electrical condition of an individuel subscriberfs line when the other lines of the system are connected to the bus-bars- The circuit may be symbolically represented vvas shown in Fig. 4 and comprises a network of three imped' ences ZW, Zil and Z1 connected in parallel. The e'lfct produced in a given line of impedance Z1 will de end upon the voltage at the terminals J. an 2 of the dia am of Fig. 4. Obviously, if one of the ines whose composite impedance is representedby Z,D is open circuited. s. change-lin the composite impedance will. occur. If the impedance Z1 were large as compared with ZM, it is obvious that s ehange'in the impedance of the latter willfsect the current owing in Z1. 0n the other hand, if the im dance Za were zero, a change in the impe snee ZM, would have n effect upon the current flowing through Z1. The latter condition is a. proximated by reason of the feet that t c impedance Zi is very smell compared with' ZM, being only 2.5 ohms in the assumed case;

llO

Consequently, a change in the impedance Z loes not appreciebly affect the single linov represented by Z1. From similar considera* tions it will also be apparent that if any one of the lines mekingup the composite impedunbe 2. be shortcircuited at some point sui*-A ii'ciently distant from the bus-bars, so that it does not amount to e ded shortcircuit across the terminals 1 and 2 of Fie. 4, no oppreciable eilect will be produced: u' on' the line Whose im edsnce is represente by Z1. 1t will also apparent that if any line conreo nected to the bus-bar is subject to interfer ence, the voltage or current so induced in itwill be largely prevented from a pearing in any other circuit by the very ow impedance Za which is bridged across the bus-baru It will be obvious that ythe general principles herein disclosed may be embodied in many other organizations Widely dif-- ferent from those illustrated Without departing from the spirit of the invention as del-ined in the following claims. f

What is claimed is:

1. In a program distribution system, a program source, an amplifier to amplify currents from said source and impress them upon bus-bars, a variable number of subscribers lines connected to said bus-bars, and means to make the impedance looking into the output of said amplier small as compared with the com o site impedance of said subscribers lines W ien all of the lines are connected to the bus-bars.

2. In a program distribution system, a program source, an amplifier to amplify currents from said source and impress them upon bus-bars, a variable number of subscribers lines adapted to be connected in parallel to said bus-bars, and a transformer etween said bus-bars and said amplifier mission lines arranged to be associated with the output of said amplifier, and means whereby the impedance looking into the output circuit of said amplifier will be small as compared with the composite impedance oli the transmission lines. y 4. In a signaling system, a transmis's'on circuit, an ampliiier included therein, a 4{variable number of transmission lines adapted to be connected to the output circuit olfsaid amplifier, and a transformer between said. lines and said ampliierI having a ratio such that the impedance looking intot'nf; output of said amplifier will be small as (dmpared with the composite impedance of Iht ie transmission lines.

In testimony whereof, I have lsigned my name -to this specification this 1st day of September, 1923.

MAURICE E. STRIEBY. 

